Cellulose is one of the most abundant carbohydrates in the plant kingdom and comprises at least one-third of the bulk of most plant tissues. In its biological cycle, cellulose is ultimately decomposed by microorganisms. Current studies of cellulases from various microorganisms are very extensive as illustrated by the ample literature in this area (See Coughlan, M. P. Biotechnol. Genet. Eng. Rev. 3:39-109 (1985); Saddler, J. N. Microbiol. Sci. 3:84-87 (1986); and Yu, I. K. and R. E. Hungate Ann. Rech. Veter. 10:251-254 (1979)). Several cellulase genes from Clostridium (Beguin et al., Bio/Technol. 1:589-594 (1983); Cornet et al., FEMS Microbiol. Lett. 16:137-141 (1983); and Millet et al., FEMS Microbiol. Lett. 29:145-149 (1985)) and other microorganisms (See Barros, M. E. C. and J. A. Thomson J Bacteriol. 169:1760-1762 (1987); Fukumori et al., J. Gen. Microbiol. 132:2329-2335 (1986); and Gilkes et al., J. Gen. Microbiol. 130:1377-1384 (1984)) have been cloned and sequenced (Beguin et al., J. Bacteriol. 162:102-1-5 (1985) and Fukumori et al., J. Bacteriol. 168:479-485 (1986)). It is of interest to study these enzymes from the perspective of their physiological and biochemical activity and evolution.
In spite of the extensive prior studies, most of the cellulases isolated from bacteria are not capable of digesting untreated natural materials such as bamboo fibers, plant cellulose, rice straw and sawdust. The dry matter of rice straw consists of cellulose, silica and lignin. In particular, lignocellulose, the material forming the woody cell wall of many plant tissues, cannot be hydrolyzed by most bacteria enzymes. While it has been reported that some cellulolytic fungi can degrade wood chips, their capabilities of digestion are limited to chips which have been pretreated with high pressure steam.
Some animals such as the giant panda live on bamboo as their primary diet. Since lignocellulose is known to be one of the major components of bamboo fibers, it is contemplated herein as part of the present invention that the panda may possess an unique mechanism in their digestive system by which lignocelluloses are digested and utilized as daily nutrients.
In light of the foregoing, there is a need for microorganisms capable of producing high levels of cellulases suitable for degradation of untreated natural materials such as bamboo fibers, plant cellulose, rice straw and sawdust. In addition, there is a further need to characterize such cellulases to gain an understanding of the biochemical mechanism for degradation of lignocellulose.